This application claims the priority of German patent document 199 42 916.2, filed Sep. 8, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a method for producing foamable metal compacts. A compact body is produced from a powder mixture comprising (1) at least one powdered metal; and (2) at least one blowing agent in powder form which yields gas when heated to a temperature equal to or above the breakdown temperature of the blowing agent.
The present invention furthermore relates to an apparatus for producing expandable metal, comprising (1) means for feeding a powder mixture containing at least one metal powder and at least one blowing agent in powder form; (2) means for producing a compact body from the powder mixture; and (3) means for heating the compact body to a temperature equal to or above the breakdown temperature of the blowing agent.
The present invention also relates to the metal foams obtained from the foamable metal bodies, also as a component of moldings and laminates.
The industrial production of metal foams or porous metal bodies has long been known. For example, in U.S. Pat. No. 3,087,807 a method for producing metal foams is described. A metal powder is mixed with a blowing agent and compacted cold under a pressure of greater than 80 MPa and then transformed by extrusion so that the particles are tightly bonded together (i.e., welded). The temperature during the extrusion must be below the breakdown temperature of the blowing agent. The extruded rod is then heated in a mold to at least the melting temperature of the metal. The rod is thus expanded to form a porous metal body. The foaming can be done in various ways, so that the finished porous metal body has the desired shape.
In German Patent DE 40 18 360 C1, a production process for porous metal bodies is disclosed wherein at least one metal powder and at least one blowing agent in powder form are mixed together and the mixture is shaped by hot compaction to a half-product. To foam the half-product, it is then heated to a temperature above the breakdown temperature of the blowing agent, preferably in the temperature range of the melting point of the metal. Then, a cooling of the body thus expanded takes place.
In German Patent DE 41 01 630 C2, a method for manufacturing foamable metal bodies is disclosed, in which the temperature is made so high during the compacting process that the bond between the individual metal powder particles is formed by diffusion, and the pressure is made so high during the hot compaction that the expansion of the blowing agent is prevented.
The known methods are still not satisfactory in every respect, and especially the range of variation that is available is not satisfactory.
The present invention is addressed to the problem of devising a method and an apparatus of the kind described above, by which the production of foamable metal bodies is simplified and/or the variability in the production of foamable metal bodies is increased.
This problem is solved by the method of the present invention wherein the production of the compact body is performed by the thermal spraying of the powder mixture by high-velocity flame spraying or cold-gas spraying.
The problem is solved by the apparatus of the present invention wherein the means for the production of the compact body from the powder mixture include an apparatus for thermal spraying by high-velocity flame spraying or by cold-gas spraying.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.